1. Field of the Invention
The present invention relates to a laser printing method for laser printing a multipack paper packaging material or other base material for packaging a plurality of containers and a laser printing system for working that method.
2. Description of the Related Art
Can containers filled with beverages, for example, beer and other alcoholic beverages are sometimes packaged together by a paper packaging material or other base material and sold as multipack packages. The can containers are printed with the best consumed by date of the beverage filled in the can containers. This printing often is performed by employing the ink jet system of spraying liquid ink to the can bottoms by a nozzle for printing. Further, when the beverage filled into the can containers is an alcoholic beverage, a warning like “alcoholic beverage” is often printed. This printing is often performed by employing a system of 3D printing embossing the can lid so as to enable the fact that the beverage filled in the can container is an alcoholic beverage to be recognized even when the purchaser is sight impaired.
On the other hand, the paper packaging material or other base material for packaging the containers itself is often not printed with the above best consumed by date. Further, the warning is often displayed printed in advance on the base material surface.
For this reason, when the purchaser is sight impaired, he or she cannot determine by touch if the beverage to be purchased is before the best consumed by date or that it is an alcoholic beverage, so might purchase beverages past the best consumed by date or alcoholic beverages mistaken for nonalcoholic beverages. To avoid such a situation, the base material of the multipack package itself is preferably also given the best consumed by date and/or the warning. However, in this case, 3D printing is necessary to enable the sight impaired to read it.
To give 3D printing, the method of 3D printing by using a laser printing system which makes ink of a layer on the surface side of a plurality of layers partially melt by heat may be considered. Such a laser printing system is disclosed in Japanese Patent Publication (A) No. 10-138641, Japanese Patent Publication (A) No. 9-175013, and Japanese Patent Publication (A) No. 9-123607.
In this regard, to display the best consumed by date or “alcoholic beverage” on a multipack package, it is preferable to first package a plurality of can containers together to form a multipack package, then print on it. Therefore, the above-mentioned laser printing system is preferably installed in the middle of the conveyor over which the multipack packages are conveyed and near the downstream side of the conveyor of the multipack packaging machine packaging a plurality of can containers together to form multipack packages. On the other hand, the conveyor is connected at its upstream side to an accumulating device in which a plurality of can container are temporarily stored and at its downstream side to a caser for placing the multipack packages in boxes.
The conveyance speed of a conveyor is controlled by a control system and changes in accordance with the states of the upstream side accumulating device and downstream side caser. For example, when the number of containers in the accumulating device is large and when the number of multipack packages before being placed into boxes at the caser is small, the conveyance speed of the conveyor is made larger. Conversely, when the number of containers in the accumulating device is small and when the number of multipack packages before being packed into boxes at the caser is large, the conveyance speed of the conveyor is made smaller or the conveyor is stopped in some cases. Further, when the caser begins operating abnormally, the conveyor may sometimes make an emergency stop.
In this way, the conveyance speed of a conveyor changes, so situations may be envisioned where the conveyor and multipack package stop at the start position of laser printing. In this case, the laser printing system will repeatedly print on the identical multipack package several times, so the identical multipack package will be partially or completely printed twice with the same words. Such a multipack package will be judged as failing in the later step of inspection of appearance.
The present invention was made in consideration of this situation and has as its object the provision of a laser printing method enabling prevention of the same base material being printed a plurality of times and a laser printing system for working this method.